In any community emergency situations may occur that will affect some portion of the persons living there. These emergency situations may range from relatively minor and localized occurrences, such as small fires, oil spills and traffic accidents that tie up major highways, to major catastrophes such as hurricanes, refinery and chemical plant fires and train wrecks. In many cases, utility power lines may be rendered inoperative, so that commercial radio and television receiving sets will not be usable. In some instances telephone systems are damaged and persons cannot be reached to be warned or called for duty as firemen and police officers, and nurses.
It would be desirable to have available in a community an emergency alerting and warning radio communications system that is always operable to receivers in residences, offices, shops, vehicles, hotels and any place where persons may be present, so that all or any selected group or class of individuals can be alerted and warned of a dangerous emergency situation that is occurring or is imminent, and to convey a message with instructions appropriate or helpful to the persons. Thus an entire town can be told to evacuate their homes because of an approaching hurricane in an alerting and warning message sent to everyone at one time. By telephone this would be difficult and time consuming, or impossible if high winds had broken the utility power and telephone lines. The emergency radio system would enable all the police officers to be contacted at one time and told where to report. Similarly in a single radio broadcast, all the nurses in the community would be contacted and given instructions to go to the scene of disaster.
In such emergency alerting and message transmitting system, the main transmitter would be located in the community police or other durable headquarter structures with a reliable source of power such as batteries or an engine-generator set, so that it would be operable at all times. The receivers would also be provided with an alternate source of electrical power such as a battery so that it would be ready at all times to receive emergency broadcasts from the transmitter. Encoding means at the transmitter would be operable to selectively activate only those receivers it is desired to give specific messages to.